This invention relates to a clutch assembly for a motor vehicle and specifically to a clutch assembly that accommodates wear to maintain a substantially constant release load during the life of the clutch.
Typically, a clutch assembly includes a retainer assembly supported about a rotating axis and movable longitudinally along the axis. A clutch cover attaches to a flywheel for rotation about the axis and supports a pressure plate. The clutch couples the transmission to the engine by sandwiching friction discs between an intermediate plate, the pressure plate and the flywheel. A plurality of levers are connected between a retainer assembly and the pressure plates. A diaphragm spring moves the retainer assembly and thereby the levers toward the pressure plates and the flywheel. The force applied to the levers sandwiches the friction discs against the flywheel with a sufficient pressure or clamp load to transfer torque from the engine to the transmission. Clutch straps bias the pressure plates away from the flywheel toward a release or disengaged position.
During normal operation of the clutch assembly, the diaphragm spring biases the retainer assembly toward an engaged position. In the engaged position the diaphragm spring overcomes the biasing force of the clutch straps toward the release position. An additional force pulls the retainer assembly away from the flywheel, thereby releasing the levers and the pressure plates. Typically, an operator depressing a clutch pedal provides the additional force. Maintaining a uniform clamp load throughout the life of the clutch is desirable.
However, during normal use, the friction discs wear. As the friction discs wear, forces exerted on the pressure plates increases in proportion to the increased distance that the pressure plate must travel to engage the friction discs. Further, the biasing load exerted by the diaphragm spring decreases as the distance increases. The result is lower clamp loads against the driven disc resulting in less efficient transfer of torque.
Accordingly, there is a need for a clutch assembly that maintains substantially constant clamp loads throughout the life of the friction discs.
An embodiment disclosed in this application is a clutch assembly for maintaining a substantially constant clamp load and pedal effort throughout various clutch wear conditions.
The clutch assembly includes a friction discs with a width of friction material. A clutch cover fastened to a flywheel rotates about an axis and a pressure plate and intermediate plate operably associated with the clutch cover rotate with the clutch cover. The pressure plate and intermediate plate move longitudinally along the axis to engage friction discs. The pressure plate and intermediate plate are biased to a release position by a plurality of clutch straps.
A retainer bearing assembly is disposed along the shaft and rotates with the clutch cover. The retainer bearing assembly moves axially along the shaft to engage at least one lever. A diaphragm spring biases the retainer bearing assembly toward the flywheel pushing the levers against the pressure plates to cause contact between the pressure plate, intermediate plate, the friction discs and the flywheel. The biasing force of the diaphragm spring overcomes the opposing biasing force of the clutch straps and applies a clamp load against the flywheel.
During normal wear of the friction discs, a width of the friction material decreases thereby requiring the retainer bearing assembly to travel a greater longitudinal distance along the axis. The biasing load exerted by the diaphragm spring on the retainer bearing assembly decreases as the distance of travel along the axis increases. Further, the biasing load exerted by the clutch straps against the biasing load of the diaphragm spring increases as the pressure plate and intermediate plate moves closer to the flywheel. This combination results in an overall lower clamp load.
An adjusting ring is movable mounted within the clutch cover. The adjusting ring supports one end of the lever. As the friction discs wear, the adjusting ring is moved toward the pressure plate to accommodate wear. However, movement of the adjusting ring does not account for the changes in the total clamping force obtained by the interaction of the diaphragm spring against the clutch straps. The present invention utilizes a resilient plate mounted to the adjusting ring that includes a plurality of extending fingers operably associated with the retainer bearing assembly.
During operation, the resilient plate exerts a biasing force against the diaphragm spring. As the friction discs wear and the adjusting ring moves toward the flywheel, the retainer assembly engages the fingers later and later during travel between the release position and the engaged position. This results in less deflection of the fingers, and less biasing force against the diaphragm spring. Concurrently, as the adjusting ring shifts towards the flywheel, the biasing force exerted by the clutch straps increases. The increase in clutch strap biasing force is substantially offset by the decrease in resilient plate biasing force resulting in substantially insignificant changes in the combined force exerted against the diaphragm spring such that clamp loads remain substantially uniform over the useful life of the friction discs.